End-point identifiers in sip

ABSTRACT

A system and method for uniquely identifying an SIP device extends the SIP communications protocol with an end point identifier, carried for example in the header of an SIP transmission. The end point identifier is useful for routing, registration, subscription, and authentication. The end point (device) of a given user epid can be uniquely identified by creating a key from an epid and a user&#39;s address-of-record (URI). This in turn enables improved connection management and security association management when the connections/IP addresses are transient, such as when HTTPS tunneling is used.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/221,620,filed Aug. 30, 2011, which is a continuation of application Ser. No.12/169,584, filed Jul. 8, 2008, now U.S. Pat. No. 8,024,470, which is acontinuation of application Ser. No. 10/387,238, filed Mar. 12, 2003,now U.S. Pat. No. 7,412,521, which applications are incorporated hereinby reference in their entirety.

AREA OF THE INVENTION

The present invention relates generally to communication between devicesover a computer network, and more particularly, to enablingidentification and authentication of endpoint devices across thecomputer network.

BACKGROUND OF THE INVENTION

The Session Initiation Protocol (SIP) is a signaling protocol thatprovides a mechanism for a computing device to locate another device itwants to communicate with over a computer network and to establish acommunication session therewith. In particular, SIP is an InternetEngineering Task Force (IETF) standard protocol for initiatinginteractive user-sessions in a number of scenarios. For example, SIP isused for Internet conferencing, telephony, gaming, virtual reality,event notification, and instant messaging. The SIP protocol enables callsetup initiation, routing, authentication and other feature messages toendpoints within an IP domain.

Like HTTP or SMTP, SIP works in the Application Layer of the OpenSystems Interconnection (OSI) communications model. As such, SIP canestablish multimedia sessions or Internet telephony calls, and modify orterminate them. The SIP protocol can also invite participants to unicastor multicast sessions that do not necessarily involve the initiator.Because the SIP supports name mapping and redirection services, usersinitiate and receive communications and services from any location andnetworks are capable of identifying users within the network.

Although SIP has been widely implemented for various applications, thecurrent SIP protocol has a deficiency whereby there is no uniqueidentifier for a device carried in the SIP signal. The standard SIPsolution is to use the device's IP address, however, this is not anadequate solution because in many situations the device itself remainsthe same yet the device's IP address changes, as in the case of areboot.

As such, it is desirable to identify endpoint devices which are involvedin a security association (SA) (i.e., a point to point association whichis not shared across multiple devices for a user). In particular, tyingthe SA to the IP-level communication address means the SA is lost whenthe communication address changes dynamically. Having a uniqueidentifier would make it possible to re-use an existing SA forsituations where the device and user credentials have not changed.

It is also desirable to support independent send and receivecommunication addresses as in the case of using TCP as a transportwherein it is typical to use different send and receive ports. Becauseof the difference in the ports, the combination of IP address and portis not suitable for uniquely identifying the device and a single devicewould be perceived as having two different identities. Using the IPaddress alone precludes the ability to have two different SIP stacks onthe same node. As such, having a unique device identifier would enableindependent send and receive communication addresses.

It is further desirable to distinguish between multiple and single pointof presence for a user as in the case where a registrar/presence agentserver chooses to enforce policies that restrict a user to having only asingle point of presence. In such a situation, a unique deviceidentifier would be beneficial in allowing the registrar to distinguishwhen a user has registered multiple clients versus when a user hasregistered the same client multiple times with a different communicationaddress.

It is still further desirable to allow routing of a request to one ofseveral devices belonging to a particular user. In particular, it isdesirable to allow the originator of the request to target a specificdestination device and to allow a device to specify that futurecommunications within a dialog should go directly to that device even insituations where the communication address for that device changes overtime.

It is yet further desirable to support reliable communications overpotentially transient HTTPS connections. Because a unique deviceidentifier is useful for identifying peers in a TLS connection, theremote end of this connection can use the device identifier to determinethe appropriate connection to use when forwarding messages, even whenthe connection is broken and re-established. Similarly, it is desirableto use the unique device identifier to manage a reboot/restart of aclient such that changes in the communication address are differentiatedfrom changes in the device.

Thus, there is a need to extend the SIP signaling protocol for thepurpose of adding an identifier for use in uniquely identifying theend-point device to overcome these and other obstacles.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides a new schemefor uniquely identifying a SIP device by extending the SIPcommunications protocol. The extension involves a parameter typicallycarried in the header of the SIP signal. The extension, referred to asthe “End Point Identifier” or “epid,” impacts the routing, registration,subscription, and authentication logic in the client, proxy, and server.The end point (device) of a given user epid can be uniquely identifiedby creating a key from an epid and a user's address-of-record (URI).This in turn enables improved connection management and securityassociation management when the connections/IP addresses are transient,such as when HTTPS tunneling is used. Although HTTPS will be discussedin certain examples herein, it will appreciated that the transientnature of the connections or IP addresses in those embodiments is notunique to that protocol, and thus the examples are merely illustrativeand not limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims set forth the features of the present invention withparticularity. The invention, together with its objects and advantages,may be best understood from the following detailed description taken inconjunction with the accompanying drawings of which:

FIG. 1 is a is a block diagram generally illustrating an exemplarycomputer system on which embodiments of the invention may beimplemented;

FIG. 2 is a schematic diagram showing a Session Initiation Protocol(SIP) system including an SIP client (C1), a proxy server (HP1), loadbalancers (LB1, LB2 and LB3), load distributors (LD1, LD2 and LD3) andSIP registrars (HS1, HS2 and HS3) in which aspects of embodiments of theinvention may be incorporated;

FIG. 3 is a schematic diagram showing exchange of signaling messagesbetween an SIP client (C1) and the SIP registrar (HS1);

FIG. 4 is a schematic diagram showing a Session Initiation Protocol(SIP) system including SIP clients (C1 and C2), proxy servers (HP1 andHP2), load balancers (LB1, LB2 and LB3), load distributors (LD1, LD2 andLD3) and SIP registrars (HS1, HS2 and HS3) in which aspects ofembodiments of the invention may be incorporated;

FIG. 5 is a schematic diagram showing exchange of signaling messagesbetween an SIP client (C1) and an SIP registrar (HS2); and

FIG. 6 is a schematic diagram showing an exemplary RTC serverarchitecture for using an EPID via SIP according to an embodiment of theinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In some situations, it is beneficial to authenticate and identifyincoming SIP messages and sign outgoing SIP messages. However, in orderto this, there is a need to uniquely identify SIP devices such thatconnection management and security association management is improved.

Turning to the drawings, wherein like reference numerals refer to likeelements, the invention is illustrated as being implemented in asuitable computing environment. Although not required, the inventionwill be described in the general context of computer-executableinstructions, such as program modules, being executed by a personalcomputer. Generally, program modules include routines, programs,objects, components, data structures, etc. that perform particular tasksor implement particular abstract data types. Moreover, those skilled inthe art will appreciate that the invention may be practiced with othercomputer system configurations, including hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, minicomputers, mainframe computers, and thelike. The invention may be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

The following description begins with a description of a general-purposecomputing device that may be used in an exemplary system forimplementing the invention, and the invention will be described ingreater detail with reference to FIGS. 2-6. Turning now to FIG. 1, ageneral purpose computing device is shown in the form of a conventionalpersonal computer 20, including a processing unit 21, a system memory22, and a system bus 23 that couples various system components includingthe system memory to the processing unit 21. The system bus 23 may beany of several types of bus structures including a memory bus or memorycontroller, a peripheral bus, and a local bus using any of a variety ofbus architectures. The system memory includes read only memory (ROM) 24and random access memory (RAM) 25. A basic input/output system (BIOS)26, containing the basic routines that help to transfer informationbetween elements within the personal computer 20, such as duringstart-up, is stored in ROM 24. The personal computer 20 further includesa hard disk drive 27 for reading from and writing to a hard disk 60, amagnetic disk drive 28 for reading from or writing to a removablemagnetic disk 29, and an optical disk drive 30 for reading from orwriting to a removable optical disk 31 such as a CD ROM or other opticalmedia.

The hard disk drive 27, magnetic disk drive 28, and optical disk drive30 are connected to the system bus 23 by a hard disk drive interface 32,a magnetic disk drive interface 33, and an optical disk drive interface34, respectively. The drives and their associated computer-readablemedia provide nonvolatile storage of computer readable instructions,data structures, program modules and other data for the personalcomputer 20. Although the exemplary environment described herein employsa hard disk 60, a removable magnetic disk 29, and a removable opticaldisk 31, it will be appreciated by those skilled in the art that othertypes of computer readable media which can store data that is accessibleby a computer, such as magnetic cassettes, flash memory cards, digitalvideo disks, Bernoulli cartridges, random access memories, read onlymemories, storage area networks, and the like may also be used in theexemplary operating environment.

A number of program modules may be stored on the hard disk 60, magneticdisk 29, optical disk 31, ROM 24 or RAM 25, including an operatingsystem 35, one or more applications programs 36, other program modules37, and program data 38. A user may enter commands and information intothe personal computer 20 through input devices such as a keyboard 40 anda pointing device 42. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite dish, scanner, or the like.These and other input devices are often connected to the processing unit21 through a serial port interface 46 that is coupled to the system bus,but may be connected by other interfaces, such as a parallel port, gameport or a universal serial bus (USB) or a network interface card. Amonitor 47 or other type of display device is also connected to thesystem bus 23 via an interface, such as a video adapter 48. In additionto the monitor, personal computers typically include other peripheraloutput devices, not shown, such as speakers and printers.

The personal computer 20 preferably operates in a networked environmentusing logical connections to one or more remote computers, such as aremote computer 49. The remote computer 49 may be another personalcomputer, a server, a router, a network PC, a peer device or othercommon network node, and typically includes many or all of the elementsdescribed above relative to the personal computer 20, although only amemory storage device 50 has been illustrated in FIG. 1. Examples ofsuch devices according to certain embodiments of the invention will bedescribed below. The logical connections depicted in FIG. 1 include alocal area network (LAN) 51 and a wide area network (WAN) 52. Suchnetworking environments are commonplace in offices, enterprise-widecomputer networks, intranets and the Internet.

When used in a LAN networking environment, the personal computer 20 isconnected to the local network 51 through a network interface or adapter53. When used in a WAN networking environment, the personal computer 20typically includes a modem 54 or other means for establishingcommunications over the WAN 52. The modem 54, which may be internal orexternal, is connected to the system bus 23 via the serial portinterface 46. Program modules depicted relative to the personal computer20, or portions thereof, may be stored in the remote memory storagedevice if such is present. It will be appreciated that the networkconnections shown are exemplary and other means of establishing acommunications link between the computers may be used in embodiments ofthe invention.

In the description that follows, the invention will be described withreference to acts and symbolic representations of operations that areperformed by one or more computers, unless indicated otherwise. As such,it will be understood that such acts and operations, which are at timesreferred to as being computer-executed, include the manipulation by theprocessing unit of the computer of electrical signals representing datain a structured form. This manipulation transforms the data or maintainsit at locations in the memory system of the computer, which reconfiguresor otherwise alters the operation of the computer in a manner wellunderstood by those skilled in the art. The data structures where datais maintained are physical locations of the memory that have particularproperties defined by the format of the data. However, while theinvention is being described in the foregoing context, it is not meantto be limiting as those of skill in the art will appreciate that variousof the acts and operations described hereinafter may also be implementedin hardware.

Referring now to FIG. 2, the present invention is directed to amechanism for integrating a unique End Point Identifier into an incomingrequest message under the Session Initiation Protocol (SIP), e.g. toenable an SIP registrar (hereinafter referred to as a “home server”) 160a-c to respond to a request from an SIP client (C1) 112 using the sameconnections on the same route as that used by the SIP client (C1) 112 toinitiate the connection. The SIP End Point Identifier is defined in anInternet Engineering Task Force (IETF) Request For Comments (RFC) 3261,which is hereby incorporated by reference in its entirety. IETF RFC 2543is also instructive with respect to the Session Initiation Protocol, andis also incorporated herein by reference in its entirety.

By way of example, as shown by the topology in FIG. 2, in a sessioninitiation operation, a client (C1) 112 (in customer 1's network 110)that registers with an SIP home server 160 a-c sends an incoming requestmessage (e.g., SUBSCRIBE message) to the SIP home server 160 a-c. Theincoming request message travels over a computer network comprising anumber of components such as load balancers 140 a-c and loaddistributors 150 a-c. Note that although the REGISTER and SUBSCRIBEmethods are sometimes used as examples herein, the described embodimentsapply as well to any other SIP method, including but not limited toNOTIFY, BYE, ACK, CANCEL, INVITE, REFER, MESSAGE, INFO, OPTIONS, PRACK,UPDATE, and PUBLISH.

The load balancers 140 a-c are typically IP-level load balancers whilethe load distributors 150 a-c are typically application-level entities.Load distributors as discussed herein preferably embody a “locationservice” as described in the SIP protocol specification (RFC 3261). Acommon deployment is to have the client (C1) 112 use the HTTP proxyserver (HP1) 115 to make an outbound HTTPS connection to one of the IPbased load balancers 140 a-c after passing through a firewall 130. Asdepicted in FIG. 2, a connection is made with Load Balancer (LB2) 140 b.The Load Balancer (LB2) 140 b then makes an HTTPS connection to one ofthe SIP based Load Distributor servers 150 a-c. As depicted in FIG. 2, aconnection is made between Load Balancer (LB2) 140 b and LoadDistributor (LD3) 150 c. The Load Distributor (LD3) 150 c subsequentlylooks up the home server for the client (C1) 112, such as via adirectory service such as an ACTIVE DIRECTORY®, a product of MicrosoftCorp. of Redmond, Wash. Alternatively, the Load Distributor (LD3) 150 cmay use LDAP, an external database, an in-memory database, or some otherexternal data source to acquire this information. Thereafter, the LoadDistributor (LD3) 150 c makes a TCP connection to the SIP home server(HS1) 160 a and forwards the incoming request message.

With the use of the End Point Identifier, also referred to as the “epid”or “End-point ID,” the outgoing response message from the SIP homeserver (HS1) 160 a is then sent back to the client (C1) 110 using thesame connections on the same route even in situations where the firewall130 or proxy server 115 drops the connection. According to the presentinvention, the epid parameter is used in conjunction with the user URI(i.e., “Uniform Resource Identifier”) to uniquely identify an end pointdevice in the system. A device can be any user agent or SIP client. Inone embodiment of the invention, the epid parameter is generated by theend point device.

Alternatively, the epid parameter is supplied by a server. In thisembodiment, the epid is typically supplied by the registrar (e.g. homeserver (HS1) 160 a) for the user. In this embodiment, the epid value canfor example be returned to the client (C1) 110 in the 200 OK response toa request such as a REGISTER request, to then be used by the client (C1)110 in future communications.

To obtain the benefits of the epid solution across a client reboot, theepid parameter for a device is stored persistently. According to thepresent invention, generation of the epid parameter occurs the firsttime the client is initialized for a given user URI and should be savedfor subsequent uses of the client by that user. As the epid isassociated with a particular user URI, the epid parameter should bestored along with this user URI. The epid is not meaningful by itself;typically its uniqueness is only assured in combination with a user URI.

To be effective, the epid value is preferably unique for each end-pointfor a user. According to the present invention, the epid parameter canbe any encoded string or substantially random value (i.e. either randomor generated by a technique such as hashing that typically ensures a lowprobability of closely spaced repeat values if any) that follows thesyntax of a “token.” Using a sufficiently random value reduces thelikelihood of collisions where two end points chose the same end-pointvalue. In one embodiment of the invention, the epid parameter is an 8character hex encoded string of an unsigned 32-bit random value. Inanother embodiment, the epid parameter is a hex encoding of the 48-bitMAC address of the device. The persistence and substantial uniqueness ofthe MAC address ensures that the associated hex encoded string ispersistently associated with a particular device and is substantiallyunique.

After generation, the epid is used as a parameter of the SIP header. Inone embodiment of the invention, the epid is used as a parameter of theSIP From: or To:

header. It is the responsibility of the client to select/generate anepid and insert the epid parameter in the From: header of each requestit generates, such as the REGISTER request. The SIP specificationensures that the epid parameter is copied to the From: header of theresponse message for the request. Copying the epid parameter allows theoriginator's epid parameter to be available in both directions andend-to-end along the signaling path.

An example of this usage of the epid parameter is:

-   -   From: “Bob”<sip:bob@domain.com>;tag=342994;epid=2a56e788

In this example, the epid parameter is outside the angle brackets. Theepid parameter is intended to be a unique identifier for an end point ofthe user in the From: or To: URI depending on which header the epid ispresent in. According to the present invention, the epid parameter isthe same across all SIP sessions for this end point even if the tagparameter is different for each SIP session. In one embodiment of theinvention, the epid parameter is treated as an opaque token by thereceiving party. Alternatively, the epid parameter is case-insensitive.

The epid parameter provided at registration time in the From: will beinserted by the registrar in the To: header on behalf of the client whenrouting requests to that client. In general, the originator of a requestwill not know the epid for the end point of the destination of therequest. The registrar inserts the parameter when it routes the requestto the destination allowing downstream proxies to take advantage of thisinformation. In one example, in user-to-user sessions established usingthe INVITE method, the registrar copies the intended recipient's epidinto the TO header, aiding routers along the route in identifyingsecurity associations, and in executing other client-specific functions.

Turning to FIG. 3, a schematic diagram 200 showing an exemplary exchangeof signaling messages between the SIP client (C1) 110 and the SIP homeserver (HS1) 160 a (depicted in FIG. 2) according to an embodiment ofthe invention is illustrated. In one embodiment of the invention, whenthe SIP client (C1) 110 initiates registration with a Web site 112(e.g., the Acme Co. network), it does a Domain Name System (DNS) serverlookup for sip.acmeco.net and obtains the IP address for the SIP homeserver (HS1) 160 a. Since Acme Co. publishes all of its front endservers in the DNS, it is possible that the SIP client (C1) message maypass through many servers (e.g., proxy servers, load balancing servers,load distributor servers) before reaching the home server (HSl) 160 a.

As depicted in FIGS. 2 and 3, the incoming request message from SIPclient (C1) 110 passes through Proxy server (HP1) 115 via path 205.Alternatively, the incoming request message passes through a forwardingproxy in the customer network. As described above, the Proxy server(HP1) routes the incoming request message to one of the load balancingservers 140 a-c, in particular, Load Balancer (LB2) 140 b via path 210.Load Balancer (LB2) then routes the incoming request message to one ofthe load distributor servers 150 a-c, in particular, Load Distributor(LD3) 150 c via path 215. Load Distributor (LD3) 150 c looks up the homeserver information for client (C1) 112 and proxies the request to clientC1's home server (HS1) 160 a via path 220.

According to one aspect of the invention, the Load Distributor (LD3) 150c has Record-Route enabled so that it adds itself to the incomingrequest message. As such, the route for registration at the IP layer isC1-HP1-LB2-LD3-HS1 whereas at the SIP layer it is C1-LD3-HS1 because theproxy server (HP1) and Load Balancer (LB2) are not SIP servers. Usingthe route information ensures that the return path through the variousnetwork components is the same as the original path from the client (C1)112 to the home server (HS1) 160 a.

To accomplish this goal, client (C1) 112 generates an epid and insertsthe epid in the From field to uniquely identify client (C1) 112 fromother clients. The epid allows the home server (HS1) 160 a to uniquelyidentify each instance of the client (C1) 112 that registers with thehome server (HS1) 160 a. In one embodiment of the present invention, theclient (C1) 112 will also use the epid as a tag value for uniquelyidentifying the registration session. In another embodiment of theinvention, the client (C1) 112 uses the same epid across instantiationsfor the same profile. Alternatively, if persistence is difficult acrossinstantiations, the client (C1) 112 generates a new epid every time forevery instantiation.

An example of usage of the epid parameter in a REGISTER request messagesent from the client (C1) 112 to the Load Distributor (LD3) 150 c is:

REGISTER sip:sip.tradewinds.net SIP/2.0 To: C1<sip:C1@tradewinds.net>;epid=2af5c32b From: C1<sip:C1@tradewinds.net>;tag=T1C1;epid=2af5c32b Call-ID: 1 CSeq: 1REGISTER Contact: <sip:10.1.1.1:2734;transport=TLS> Max-Forwards: 70Expires: 300As can be seen from this example, the epid parameter generated and addedto the header is 2af5c32b. After the Load Distributor (LD3) 150 creceives the incoming request message, with the Record-Route enabled,the Load Distributor (LD3) 150 c adds a Record-Route header to theREGISTER request message. An example of usage of the epid parameter in aREGISTER request message sent from the Load Distributor (LD3) 150 c tothe home server (HS1) 160 a is:

REGISTER sip:sip.tradewinds.net SIP/2.0 To: C1<sip:C1@tradewinds.net>;epid=2af5c32b From: C1<sip:C1@tradewinds.net>;tag=T1C1;epid=2af5c32b Call-ID: 1 CSeq: 1REGISTER Contact: <sip:10.1.1.1:2734;transport=TLS> Record-Route:<sip:LD1.tradewinds.net:1234;transport=TCP> Max-Forwards: 69 Expires:300To send an outgoing response message from home server (HS1) to theclient (C1), the header information is parsed to identify the routeinformation.

Turning to FIG. 4, in a session subscription operation, a client (C1)112 in customer 1's network 110 has on its buddy list a client (C2) 122in customer 2's network 120. A SUBSCRIBE message is sent by client (C1)using the same steps as that described for the registration scenarioexplained with reference to FIGS. 2 and 3. The SUBSCRIBE request followsthe same route as that for registration, namely client (C1) 112 routesthe SUBSCRIBE request to the proxy server (HP1) 115 which routes therequest to the Load Balancer (LB1) 140 a which, in turn, routes therequest to the Load Distributor (LD2) 150 b. The Load Distributor (LD2)150 b then routes the request to the home server (HS2) 160 b for client(C2) 122. The Load Distributor (LD2) 150 b preferably has Record-Routeenabled so that it adds its route information to the SUBSCRIBE request.

To build the SUBSCRIBE message, the client (C1) 112 uses the epidgenerated previously in the registration function, namely 2af5c32b, andinserts the epid alihome sever (HS1) 160 a of the client (C1) 112 toidentify the instance of the client that the message (i.e., NOTIFYmessage) needs to be sent to. The PAS uses the existence of the epidparameter in the From: header as an indication that NOTIFY messages forthis subscription should be routed via the home server (HSl) 160 a forclient (C1) 112.

The home server (HSl) 160 a also uses the SIP user URI of the userinstead of the IP address in the contact field because routing of NOTIFYmessages associated with this SUBSCRIBE is done based on the currentregistration state of the client and not based on the IP address of theclient at the time the SUBSCRIBE was sent.

An example of usage of the epid parameter in a SUBSCRIBE request messagesent from the client (C1) 112 to the Load Distributor (LD1) 150 a is:

SUBSCRIBE sip:C2@tradewinds.net SIP/2.0 To: C2 <sip:C2@tradewinds.net>From: C1 <sip:C1@tradewinds.net>;tag=T2C1;epid=2af5c32b Call-ID: 2 CSeq:1 SUBSCRIBE Event: Presence Contact: <sip:C1@tradewinds.net>Max-Forwards: 70 Expires: 21600

In this case, no record-routing is required since the contact address ofthe client was set to point back to the home server. Since the routerecorded for the Registration is used for routing messages, there is noneed to Record-Route other requests. The Proxy can be configured suchthat it inserts Record-Route for REGISTER requests only, such as for usewith the RTC registrar. An example of usage of the epid parameter in aSUBSCRIBE request message sent from the Load Distributor (LD2) 150 b tothe home server (HS2) 160 b is:

SUBSCRIBE sip:C2@tradewinds.net SIP/2.0 To: C2 <sip:C2@tradewinds.net>From: C1 <sip:C1@tradewinds.net>;tag=T2C1;epid=2af5c32b Call-ID: 2 CSeq:1 SUBSCRIBE Event: Presence Contact: <sip:C1@tradewinds.net>Max-Forwards: 69 Expires: 21600

According to one aspect of the invention, when the presence state ofclient (C2) 122 changes, client (C2) 122 updates its presence stateusing a SERVICE request to its home server (HS2) 160 b. Home server(HS2) 160 b sends NOTIFY messages to all watchers of client (C2) 122which includes client (C1) 112. The home server (HS2) 160 b looks up thecontact for client (C1) 112 in order to send the NOTIFY message. In oneembodiment, the home server (HS2) 160 b finds that the contact isassociated with an epid parameter from the From header. This indicatesthat the NOTIFY message is sent to the home server (HS1) 160 a forclient (C1) 112 instead of using the Route specified in the SUBSCRIBErequest. The home server (HS2) 160 b looks up the home server for client(C1) 112 and finds that it is home server (HSl) 160 a. The home server(HS2) uses the Contact field that was received in the SUBSCRIBE requestfor the Request-URI of the NOTIFY message. The home server (HS2) theninserts the epid from the SUBSCRIBE request into the To: header of theNOTIFY and routes the NOTIFY message to home server (HS1) 160 a.

When the Load Distributor (LD2) 150 b does a lookup for the home serverof client (C2) 122, it looks up the home server for client (C1) 112 aswell and inserts it as a parameter in the SUBSCRIBE request beforerouting it to home server (HS2) 160 b. This is an optimization to avoidlooking up the home server for Cl when routing the NOTIFY request. Anexample of usage of the NOTIFY message sent by home server (HS2) 160 bto home server (HS1) 160 a is:

NOTIFY sip:C1@tradewinds.net To: C1<sip:C1@tradewinds.net>;tag=T2C1;epid=2af5c32b From: C2<sip:C2@tradewinds.net> Call-ID: 2 CSeq: 2 NOTIFY Event: PresenceMax-Forwards: 70

In an embodiment of the invention, when the home server (HS1) 160 areceives the NOTIFY message, it takes the Request-URI of the NOTIFYmessage and looks up the Registration database for all contactsregistered for that SIP URI. When the home server (HS1) 160 a finds amatch, it compares the epid in the To of the NOTIFY message with eachcontact registered for that URI. When the epids match, the home server(HS1) 160 a routes the NOTIFY using the Route stored in the Registrationinformation for that contact. The home server (HS1) 160 a then insertsthe Route header with the contact information for client (C1) 112received in the REGISTER request. In this case, the NOTIFY message isrouted from home server (HS1) 160 a to Load Distributor (LD2) 150 b toLoad Balancer (LB1) 140 a to the proxy server (HP1) 115 and then toclient (C1) 112.

Thereafter, the home server (HS2) 160 b preserves the From tag receivedin the SUBSCRIBE request and places it in the To field of the NOTIFYrequest. In this manner, the client can identify the SUBSCRIBE sessionto which the NOTIFY belongs. The home server (HS2) 160 b also preservesthe epid parameter from the From field in the SUBCRIBE request andplaces it in the To field of the NOTIFY request. If there are multipleclients for client (C1) 112 that have sent a SUBSCRIBE to the homeserver (HS2) 160 b, then the home server (HS2) 160 b sends a NOTIFY foreach instance of the client. Each instance of the client is uniquelyidentified by the epid parameter from the From field of the SUBSCRIBErequest.

An example of usage of the NOTIFY message sent by the home server (HS1)160 a to the Load Distributor (LD2) 150 b is:

NOTIFY LD1.tradewinds.net:1234;transport=TCP SIP/2.0 To: C1<sip:C1@tradewinds.net>;tag=T2C1;epid=2af5c32b From: C2<sip:C2@tradewinds.net> Route: <sip:10.1.1.1:2734;transport=TLS>Call-ID: 2 CSeq: 2 NOTIFY Event: Presence Max-Forwards: 69When the Load Distributor (LD2) 150 b receives the request, it rewritesthe Request-URI with the Route header in the NOTIFY and routes therequest over the same TLS connection that the client initiated whendoing the registration. This connection is located using the epidparameter in the To: header as shown here:

NOTIFY sip:10.1.1.1:2734;transport=TLS SIP/2.0 To: C1<sip:C1@tradewinds.net>;tag=T2C1;epid=2af5c32b From: C2<sip:C2@tradewinds.net> Call-ID: 2 CSeq: 2 NOTIFY Event: PresenceMax-Forwards: 68

An exemplary RTC server architecture 600 for using an epid via SIPaccording to an embodiment of the invention is illustrated in greaterdetail in the schematic diagram of FIG. 6. The architecture isimplemented in a number of portions. The primary portion of thearchitecture is the SIP Proxy 601. At the SIP Proxy 601, the epidparameter is used to identify a security association between the deviceendpoint and the proxy. This security association is used to signoutgoing messages and to verify the signature of incoming messages whenappropriate.

Above the proxy layer 601 is an application, the registrar 603, whichalso makes use of the epid parameter. Since the epid parameter uniquelyidentifies an endpoint for a given user, the registrar 603 examines thisparameter to easily determine whether or not a given request comes froman endpoint it has previously seen. This allows the registrar 603 tomake policy decisions regarding whether to allow the request or not. Italso allows the registrar 603 to determine the proper signaling path(connection) that it should use for forwarding requests destined to agiven user. This is particularly valuable in a situation where theconnection may be changing rapidly due to unreliable network conditionsor otherwise. Thus, the epid information is especially important forconnection management in environments that make use of NATs, firewalls,and DHCP.

The proxy 601 and/or the registrar 603 maintain a set of tables to aidin connection management. In particular, in an embodiment of theinvention, the tables include a connection table 605, a securityassociation table 607, and an endpoint data table 609. Each table isindexed by user URI and epid. These tables allow the proxy 601 and theregistrar 603 to modify their operation to account for plurality,capability, and presence of the devices associated with each user.Finally, at the lowest level, the proxy 601 and registrar 603 interfacewith the SIP protocol stack 611 which is responsible for receipt ofincoming messages 613 and transmission of outgoing messages 615.

It should be noted that although the discussion has primarily focused onthe use of epids by client devices, the same basic technique can providenumerous benefits when applied to servers as well. For example, eachserver may insert its own epid value in a Record-Route or Route header,such as, for example:

-   Route:<sip:proxy.domain.com>;lr;epid=4353536. Use of an epid    parameter in this manner confers benefits distinct from those    conferred by the use of epids with respect to clients. For example,    use of server epids allows a stateful server to indicate when it has    rebooted and lost its prior state. Moreover, server epids can    provide unique identification of a server, such as when that server    is just one of a plurality of servers in a cluster having a single    common “virtual” IP address.

In addition, the use of server epids facilitates classification of aconnection by a server as belonging to a group of connections thatshould be treated identically from the perspective of a peer connectingto that server. Finally, use of server epids allows a peer of a serverto reuse an existing connection to that server, even if the destinationIP address of the server is different, such as when the server ismulti-homed or has multiple NICs.

It will be appreciated that the unique mechanism described herein allowsfunctionality beyond that permitted by using a device's IP address asits identifier. For example, the device's IP address can change, as inthe case of a reboot, but the device identifier formed of the useridentifier and the epid can remain the same in such situations.Moreover, while tying a security association to an IP-levelcommunication address will cause the SA to be lost when thecommunication address changes dynamically, the epid allows re-use of anexisting SA for situations where the device and user credentials havenot changed.

Moreover, according to a further embodiment of the invention, use of theepid allows independent send and receive communication addresses, suchas when using TCP as a transport over different send and receive ports.In this case, an endpoint maintains two separate Session InitiationProtocol stacks, having two endpoint identifiers, so that one stack isused for sending and the other is used for receiving.

In an embodiment of the invention, the epid also allows a distinctionbetween multiple and single point of presence for a user, such as when aregistrar/presence agent server chooses to enforce policies thatrestrict a user to having only a single point of presence. In such asituation, the epid allows the registrar to distinguish between a userwith multiple registered clients and a user who has registered the sameclient multiple times with a different communication address.

The epid moreover allows the originator of a request to target aspecific destination device in an embodiment of the invention and allowsa device to specify that future communications within a dialog should godirectly to that device even in situations where the actualcommunication address for that device changes over time. Finally, theepid also supports reliable communications over potentially transientHTTPS connections in an embodiment of the invention. In particular, theremote end of a TLS connection can use the epid to determine theappropriate connection to use when forwarding messages, even when theconnection is broken and re-established.

Illustrative embodiments of the present invention and certain variationsthereof have been provided in the Figures and accompanying writtendescription. The present invention is not intended to be limited to thedisclosed embodiments. Rather the present invention is intended to coverthe disclosed embodiments as well as others falling within the scope andspirit of the invention to the fullest extent permitted in view of thisdisclosure and the inventions defined by the claims appended hereinbelow.

1. (canceled)
 2. A method comprising: receiving a Session InitiationProtocol compliant request at a receiving endpoint from a transmittingendpoint, the Session Initiation Protocol compliant request including anendpoint identifier and user information, wherein a combination of theendpoint identifier and the user information uniquely identifies thetransmitting endpoint within a network independently of an InternetProtocol (IP) address of the transmitting endpoint.
 3. The method ofclaim 2, wherein the Session Initiation Protocol compliant request isconstructed at the transmitting endpoint.
 4. The method of claim 2,wherein the endpoint identifier is an encoded string representing ahardware address of the first endpoint.
 5. The method of claim 2,wherein the request is associated with a SIP method selected from thegroup of methods consisting of: REGISTER; SUBSCRIBE; NOTIFY; BYE; ACK;CANCEL; INVITE; REFER; MESSAGE; INFO; OPTIONS; PRACK; UPDATE; andPUBLISH.
 6. The method of claim 2, wherein the endpoint identifier isgenerated by a registrar remote from the first endpoint.
 7. The methodof claim 2, further comprising, after receiving the Session InitiationProtocol compliant request, transmitting subsequent communications fromthe receiving endpoint to the transmitting endpoint.
 8. The method ofclaim 7, wherein the transmitting endpoint is among a plurality ofendpoints associated with the user information.
 9. The method of claim2, wherein the Session Initiation Protocol compliant request is receivedfrom the transmitting endpoint via a proxy server.
 10. The method ofclaim 2, wherein the user information includes a uniform resourceidentifier associated with the user.
 11. The method of claim 2, furthercomprising transmitting a response to the request using a transmissionaddress, wherein the transmission address comprises the endpointidentifier.
 12. A system comprising: a transmitting endpoint comprising:a processing unit; a memory operatively connected to the processing unitand storing instructions executable on the processing unit, theinstructions causing the transmitting endpoint to, when executed:construct a Session Initiation Protocol compliant request fortransmission to a receiving endpoint, the Session Initiation Protocolcompliant request including an endpoint identifier and user information,wherein a combination of the endpoint identifier and the userinformation uniquely identifies the transmitting endpoint within anetwork independently of an Internet Protocol (IP) address of thetransmitting endpoint; and transmit the request to a receiving endpoint.13. The system of claim 12, further comprising the receiving endpointpositioned remotely from the transmitting endpoint, the receivingendpoint communicatively connected to the transmitting endpoint.
 14. Thesystem of claim 13, further comprising a proxy server communicativelyconnected between the transmitting endpoint and the receiving endpoint.15. The system of claim 12, wherein the Session Initiation Protocolcompliant request includes routing information describing a path betweenthe transmitting endpoint and the receiving endpoint.
 16. The system ofclaim 12, wherein the transmitting endpoint is further configured togenerate the endpoint identifier.
 17. The system of claim 12, whereinthe transmitting endpoint comprises a server.
 18. The system of claim17, wherein the server includes a plurality of network interfaces, andwherein the endpoint identifier is associated with one of the pluralityof network interfaces.
 19. The system of claim 12, wherein thetransmitting endpoint comprises a client device.
 20. The system of claim12, wherein the request is transmitted to the receiving endpoint via aHTTPS connection.
 21. A computer-readable storage medium comprisingcomputer executable instructions stored thereon which, when executed bya computing system acting as a transmitting endpoint, cause thecomputing system to perform a method comprising: constructing a SessionInitiation Protocol compliant request for transmission to a receivingendpoint, the Session Initiation Protocol compliant request including anendpoint identifier and user information, wherein a combination of theendpoint identifier and the user information uniquely identifies thetransmitting endpoint within a network independently of an InternetProtocol (IP) address of the transmitting endpoint; and transmitting therequest to a receiving endpoint.